Letter

The purpose of this prospective cohort study was to clarify the incidence and kinds of medical comorbidity for which psychiatric patients should be hospitalized. Gathering such epidemiological data in Tokyo, which has approximately 12 million inhabitants, might inform public policy not only in Japan but also in other countries.

The study was conducted throughout Tokyo from April 1 to May 31, 2007. Participating in the study were 21 of Tokyo's 28 general hospital psychiatric units (75%), all three general hospital psychiatric emergency units, and all 11 general hospital psychiatric units specializing in medical comorbidity. Because these three types of general hospital psychiatric units are responsible for treating severe medical illness among psychiatric patients in Tokyo, the study was designed to capture all psychiatric patients admitted for primary medical diagnoses. Information was collected about demographic and clinical characteristics of patients who were admitted and those who were not admitted because no beds were available. The study protocol was approved by an institutional review board.

In the two-month period 326 patients were admitted to one of these units for a primary medical diagnosis: 174 to general hospital psychiatric units, ten to general hospital psychiatric emergency units, and 142 to general hospital psychiatric units specializing in medical comorbidity. The mean±SD age of these patients was 61.7±16.2 years, and 150 patients (46%) were male. Of the 326 patients, 194 (60%) were medical cases and the remaining 132 patients (40%) were surgical. Respiratory diseases were the most frequent (61 patients, or 19%), followed by diseases requiring orthopedic surgery (42 patients, or 13%), diseases requiring abdominal surgery (32 patients, or 10%), and gastrointestinal and hepatic diseases (32 patients, or 10%). At discharge 130 patients (40%) had ICD-10 psychiatric diagnoses in the F2 category (schizophrenia and schizotypal and delusional disorders), 91 patients (28%) had ICD-10 F0 diagnoses (organic mental disorders, including symptomatic disorders), and 149 patients (15%) had ICD-10 F3 diagnoses (mood disorders). Among the patients with F0 diagnoses were 59 patients (18%) with dementia and organic amnesic syndrome (F00–F04) and 32 patients (10%) with delirium and other disorders (F05–F07). A total of 88 patients could not be admitted to general hospital psychiatric units because there were no available beds.

On the basis of the number of patients who were admitted to general hospital psychiatric units (174 patients) and the participation rate for that type of unit in the study (75%), the estimated total number of patients admitted to that type of unit during the study is 232. Also, on the basis of the number of patients who weren't able to be admitted to that type of unit (88 patients) and the participation rate (75%), the estimated total number of patients who could not be admitted to that type of unit during the study is 117. The numbers of patients admitted to general hospital psychiatric emergency units and general hospital psychiatric units specializing in medical comorbidity were ten and 142, respectively. The participation rates for both of these types of unit were 100%, and there were no patients who were not able to be admitted.

Thus a total of 501 patients needed admission over the study period, which suggests an annual total of 3,006 patients. Thus with approximately 12 million inhabitants, the incidence of medical comorbidity for which psychiatric patients should be hospitalized appears to be at least 25 per 100,000 inhabitants in Tokyo.

Although previous studies have examined comorbid medical conditions among psychiatric inpatients ( 1, 2 ), these studies looked at hospitals only and did not use population-based designs ( 1, 2 ). One population-based study focused only on mortality among psychiatric outpatients ( 3 ). Thus few cohort studies about hospitalization for medical comorbidities among patients with severe mental illness have been conducted. One strength of our study is that it included all psychiatric patients who lived in a defined area during the study period. A limitation is that our findings may be representative only of patients in Tokyo.

This work was supported by grant H-19-009 from the Ministry of Health, Welfare, and Labor of Japanese Government.

The authors report no competing interests.

Dr. Hatta and Dr. Arai are with the Department of Psychiatry, Juntendo University School of Medicine, Tokyo. Dr. Kurosawa is with the Nippon Medical School in Tokyo.